A crankshaft drives the front end assembly drive (FEAD) system of an engine. The crankshaft is turned by the firing of pistons, which exerts a rhythmic torque on the crankshaft, rather than being continuous. This constant application and release of torque causes vacillations, which can stress the crankshaft to the point of failure. Stated another way, the crankshaft is like a plain torsion-bar, which has a mass and a torsional spring rate, that causes the crankshaft to have its own torsional resonant frequency. The torque peaks and valleys, plus the inertia load from the acceleration of the reciprocating components, cause the crankshaft itself to deflect (rotationally) forward and backward while it is operating. When those pulses are near the crankshaft resonant frequency, they cause the crank to vibrate uncontrollably and eventually break. Accordingly, a torsional vibration damper (sometimes referred to as a crankshaft damper) is mounted on the crankshaft to solve this problem by counteracting torque to the crank, negating the torque twisting amplitude placed upon the crankshaft by periodic firing impulses, and to transfer rotational motion into the FEAD system, typically by driving an endless power transmission belt.
Torsional vibration damper hubs are expected to be as light, strong, and cost effective as possible. The traditional means of producing a hub in the United States has been through casting the hub with either Nodular or Gray Cast Iron and then machining it to its final shape. However, this method of production has to keep a keen eye of the castability of the material (i.e. filling the mold, and not causing voids etc.) which then leads to a structure that is usually heavier than necessary.
There are other means of production employed elsewhere in the world that yield much lighter and cheaper designs such as stamping and/or forming the hub. However, these methods do not allow for the incorporation of a seal nose because the material used in these processes is soft and does not provide sufficient abrasive/wear resistance needed because of the wear experienced by the seal nose. Some European designs have incorporated a two-piece construction (one of a formed soft steel for the main body of the hub and the other of a hardened or tough steel for the seal nose area) that are welded together to provide axial and angular integrity to the structure. Welding requires specialized capital investment in equipment and is esthetically unappealing, which makes welded two-part hub constructions more difficult to sell in the U.S. market.